Single in-line memory module (SIMM) sockets are well-known devices for interconnecting printed circuit boards (PCB's). The SIMM sockets have an elongated channel and a plurality of electrical contacts extending into the channel along its length. An edge of one PCB (the daughterboard) is insertable into the channel, whereby circuit edge pads of the daughterboard are engaged by the contacts of the SIMM socket. The contacts have leads which extend below a bottom surface of the SIMM socket for electrical connection with circuit paths on a mating PCB (the motherboard). Such electrical connection may be by lead posts which extend through plated through-holes in the motherboard, or by surface mount leads which engage and are connected to contact pads on the motherboard in a soldering operation. With either through-hole or surface mount leads, alignment of the leads with their respective circuit paths on the motherboard is critical.
A SIMM socket is typically retained to the motherboard by one or more plastic retention posts which are integral with and extend from a bottom of the socket. These retention posts are dimensioned to resiliently engage in holes in the motherboard. Due to the inability of circuit board manufacturers to maintain close tolerances on circuit board thickness and hole diameter, it is difficult to consistently achieve secure retention and precise alignment of the SIMM socket on the PCB. This is particularly a problem with SIMM sockets having surface mount contacts, because the leads of these contacts must be in abutting engagement with their respective contact pads on the motherboard in order that the leads can be soldered to the contact pads. If the circuit board thickness and hole diameter are not held to close tolerances, the SIMM socket may be loosely held on the circuit board.
A particular problem arises in the case of SIMM sockets having through-hole leads which are wave soldered to the motherboard. The motherboard is heated on the underside away from the socket and, because of thermal expansion, the board pulls away from the socket creating a gap between the board and the socket. The solder freezes while this relative condition exists and, when the board cools and returns to thermal equilibrium, the board imparts a bow in the socket such that a gap is created between a central portion of the socket and the board. What is needed is a retention device that will firmly hold a SIMM socket to a circuit board despite thermal stresses and relatively large tolerances on circuit board thickness and hole size.
In addition to the plastic retention posts normally used for retaining SIMM sockets to circuit boards, other devices referred to generally as boardlocks are known for removably securing a socket-type electrical connector to a circuit board. The boardlocks typically have a first portion including means for engaging in the connector housing, and a second portion including means for engaging in a hole in the circuit board. While these devices are known in various configurations and are generally satisfactory for their intended use, it would be advantageous to have an improved boardlock that is tolerant of relatively large variations in circuit board dimensions.
The present invention provides a boardlock of simple yet robust construction which assures that a socket is retained fifthly to a circuit board in spite of relatively large discrepancies in circuit board thickness and hole size due to large manufacturing tolerances.